Surface materials or covering materials for automobile interior, such as instrument panels, door trims, a console box, arm-rest, head-rest, require lightness, high quality, complex and elaborate shape, and now also impact resistance. Using instrument panels as an example, these panels have numerous openings, and while separable door-type passenger-seat air bags had been used previously, the use of concealed passenger-seat air bags has been on increase recently for improved appearance and simplicity of process.
For the conventional surface materials or covering materials for automobile interior, there are vacuum-molded materials made of polyvinyl chloride (hereinafter referred to as “PVC”) resin and acrylonitrile-butadiene-styrene-copolymer resin (hereinafter referred to as “ABS”) sheets, powder-molded materials made of PVC resin and plasticizer, sol-molded materials made of paste PVC resin and plasticizer through emulsion polymerization, and vacuum-molded materials made of TPO sheets.
However, with regard to environmental preservation, environment-friendly materials that can be recycled and do not generate pollutants during incineration are highly required. The materials including the PVC resin are not easily recyclable and generate acidic substances during incineration. Also, it is hard to reduce the weight because the PVC resin has a high specific gravity. And, PVC-based compositions are not suitable for concealed air bags because improvement of cold-resistance by adding plasticizers is limited.
Vacuum-molded materials made of PVC sheet and TPO sheet do not have a good finishing touch due to low surface hardness. Therefore, patterns like embossing are easily effaced. Also, it is difficult to make a PVC sheet or a TPO sheet into a complex shape, and the materials may be deformed with time due to the residual stress during molding. While the sol-molded materials have a good softness, there are still problems of variation in thickness and flow marks. Moreover, the raw materials cannot be stored for a long time due to the change in sol viscosity and other properties.
Recently, a TPO composition capable of powder-molding was developed. For example, Korean Patent Nos. 95-12102 & 95-12106 disclose an elastomer composition comprising ethylene-α-olefin copolymer rubber (containing mineral oil) partially crosslinked with polyolefin resin. However, pinholes may be formed and the flatness is poor because this composition has a low melt fluidity. Further, because of the hardness necessary to ensure good mechanical properties, other properties such as the tensile strength, low-temperature flexibility, cold-resistance and softness are poor. In addition, the folding during demolding is not restored because the molded material is hard, thereby leaving permanent folded marks.
A cost-effective thermoplastic elastomer composition that has the right combination of strength, hardness, cold resistance, moldability, and foldability so that it is useful for car interior surfaces is needed in the industry.